1. Field of the Invention
The present invention relates to a screen printing apparatus.
2. Description of the Conventional Art
A conventional screen printing apparatus is, for example, as shown in FIGS. 11(a)–11(d), constituted by a base plate 101 in which a substrate to be printed 102 is mounted, and a screen printing plate 103 provided in a tensional manner on the base plate 101 is substantially parallel to an upper surface of the base plate, and is structured such as to pass a printing paste 105 supplied on the screen printing plate 103 by a paste supplying means 106 in a manner shown in FIG. 11(a) through a pattern hole (not shown) of the screen printing plate 103 due to a movement of a squeegee 104 as shown in FIG. 11(b), thereby forming a pattern on the substrate to be printed 102. In this case, FIG. 11(c) is a view showing a state that a movement of the squeegee reaches a terminal end, and FIG. 11(d) is a view showing a state of moving the squeegee in an opposite direction so as to start printing.
In this case, in order to stably executed the screen printing, it is necessary to control a viscosity of the paste, a performance of the screen printing plate (a thickness of the screen printing plate, a tension balance, an accuracy, a strength, a service life and the like), a performance of the squeegee (an accuracy, a hardness, an angle and the like), a mechanical performance (an accuracy, a speed control and a pressure control) and the like so as to always keep in a uniform state.
However, in the conventional screen printing apparatus mentioned above, since the paste 105 is applied to all over the screen printing plate 103 in an exposed manner, the following problems are provided.
{circle around (1)} Since a lot of expensive paste which costs between some tens of thousand yen and some hundreds of thousand yen is left on the screen printing plate, a lot of loss money is generated.
{circle around (2)} Since the paste is directly supplied onto the screen printing plate, a lot of time is required for changing the paste, so that an operation efficiency is largely reduced.
{circle around (3)} Since the paste is exposed to an air so as to be oxidized and a property is deteriorated, an electric property and the like after printing are deteriorated.
{circle around (4)} Since a solvent mixed in the paste is evaporated and the viscosity is changed, a printing property is significantly deteriorated.
{circle around (5)} Since the evaporated solvent has a strong odor, a problem relating to an environment pollution is generated.
{circle around (6)} Since the viscosity of the paste is changed due to an influence of a temperature change, a printing performance is significantly deteriorated.
{circle around (7)} Since dusts are mixed within the paste, the pattern formed by the printing is disconnected and shorted. Then, in order to carry out a countermeasure thereof, a clean room which is expensive and hard to be controlled is required.
Further, in order to solve the problem mentioned above, in Japanese Unexamined Patent Publication No. 6-210829, as shown in FIG. 12, there is proposed a method of charging a printing paste 205 within a chamber 209, supplying and recovering the paste 205 through a supply port 207 which can be opened and closed, by rotating a roller 206, and printing by a front blade 208. In this case, reference numeral 202 denotes a substrate to be printed, reference numeral 203 denotes a screen printing plate and reference numeral 204 denotes a rear blade.
However, in this method, the following problems are provided.
{circle around (1)} Since the paste is supplied due to a rotational force of the roller 206, it is necessary that the roller 206 and the paste are directly in contact with each other, so that a lot of time is required for cleaning and maintaining the roller.
{circle around (2)} Since the paste 205 is directly supplied within the chamber 209, it is necessary to carry out a maintenance such as a periodical cleaning or the like, so that a long time is required for the maintenance operation.
{circle around (3)} Since the paste 205 is directly supplied within the chamber 209, a lot of time is required for changing the paste, so that an operation efficiency is largely reduced.
{circle around (4)} Since a lot of expensive paste which costs between some tens of thousand yen and some hundreds of thousand yen per 1 kg is left within the chamber 209, a lot of loss money is generated.
{circle around (5)} Since an air is mixed at a time of supplying the paste 205 within the chamber 209, a defect such as a wire disconnection, a chip or the like is generated in a pattern after printing.
{circle around (6)} Since an inner portion of the chamber 209 is exposed to the air, the paste is oxidized or deteriorated.
{circle around (7)} It is necessary to control an elastic force of the squeegee, a wetting property of a surface of the squeegee and the like in correspondence to a property of the paste, however, in this example, since the squeegee is executed by the front blade 208 constituted by a thin plate metal, it is possible to adjust only on the basis of the metal, so that it is impossible to adjust a suitable elastic force.